1. Field of the Invention
This invention relates to a method for forming a color image by using photoconductive toners and, more particularly, to a method for forming a highly sensitive color image by one shot of exposure to image-wise light.
2. Description of the Prior Art
Heretofore, various methods are known in the art for producing hard copies for preserving and handling electrical color image signals.
For example, it is known to provide colors corresponding to the image signals to the recording paper at coordinate positions thereof corresponding to original color signals, as for instance by spraying ink of a predetermined color (ink jet printing) or thermally developing a color on the recording paper (thermal coloring). In these methods, since coloring means are caused to mechanically sweep the recording paper along coordinate axes thereof for sequential image formation, a prolonged sweep time is required for producing an accurate color image. Moreover, a limitation is placed on the power of resolution as a function of the properties of the coloring means employed.
An electrophotographic process is also known in the art for shortening the image forming time interval and improving the power of resolution. However, in the conventional color electrophotographic process, three color toners are sequentially exposed, developed and fixed in three separate steps, thus complicating the image forming operation. Moreover, color filters are required for color separation, thus complicating the apparatus. In addition, there is the risk of color deviation from the original color.
For producing a color image by one shot exposure to light, methods are also known in the art by which particles containing colorless sublimable dyes are electrostatically deposited on a sensitized plate or photosensitive particles containing colorless sublimable dyes are electrostatically deposited on a photoconductive plate, after which the particles are exposed to light so that the dyes are caused to develop their color on the transfer sheet. In these methods, color images can be formed only on a special transfer sheet provided with a coloring layer of deposited organic or inorganic acids for coloring the colorless sublimable dyes, thus causing elevated costs. In addition, there is the risk of color fading because the dyes are only poor in durability.